The present invention relates to a vehicle brake system with an electronically controllable brake booster.
For vehicle brake systems with brake boosters there is the requirement to complete a braking operation initiated by the driver in an optimum manner, even then when the driver""s reaction is not always appropriate to the prevailing situation. For this purpose, electromagnetically operable auxiliary air controllers were provided which were activated dependent on the actuation dynamics of the brake pedal (see applicant""s postpublished applications P 42 17 409 and P 43 09 850).
From DE-OS 39 02 215 a vacuum brake booster is known where a contact switch is provided in the range of the stroke of a valve piston in the control valve housing. The first contact of this contact switch is formed as a metallic ring which engages a recess in the control valve housing. The second contact is formed by the valve piston itself, with an axially movable metallic contact member being guided in a guide sleeve arranged in the ring and made from an insulating material, which is biassed by means of a compression spring and provides for an electric connection between the ring and the valve piston. A valve is connected with two contact elements embedded in the control valve housing, with the contact element cooperating with the valve piston being biassed by means of a compression spring against the valve piston. The compression spring is thereby constantly subjected to tension so that the connection between the working chamber of the brake booster and the vacuum source is free. In the case of an actuation the valve member is lifted off the ring so that the current supply to the valve and consequently the connection between the working chamber and the vacuum source are interrupted.
From EP 0 327 276 a brake booster is known where a switching means is arranged adjacent to the valve element for activating brake lights and a stop element is carried by the valve element, with the switching means being activated dependent on a movement of the stop element together with the valve element. The assembly including the switching element is attached to a housing of the brake booster which contains the servo cylinder.
From EP 0 379 329 a brake booster is known where a switch with two contacts is arranged in the housing of the brake booster. An actuation member axially displaced by the brake pedal has a laterally projecting bar which can bridge the two contacts and thus close the circuit.
From postpublished P 44 00 688.8 a vehicle brake system with an electronically controllable brake booster is known, which comprises an actuation member transmitting the actuation travel of the brake pedal to a master cylinder, which is allocated a travel limiting element, limiting the axial actuation travel of the actuation member, in that it is accepted between two stops.
In order to positively and trouble freely detect an abortion of an emergency braking desired by the driver, with this arrangement a switching elemente can be activated by the travel limiting element together with one of the stops, which upon contact between the travel limiting element and said stop issues a signal to the controller of the brake booster.
It is thereby achieved that by the driver""s release the brake pedal only the switching element is activated in such a manner that it initiates a signal which is supplied to the electronic controller of the vehicle brake system in order to cancel the maximum level control of the brake power (as it is taught in the above state of the art).
This arrangement is, however, expensive in that a precisely defined switching point is difficult to establish due to the tolerances and assembly inaccuracies.
The present invention is therefore based on the problem to provide an easy to assemble and space saving arrangement that has the capability to compensate the tolerances so that the switching point can be reliably established.
To solve this problem the initially mentioned apparatus is characterized by the characteristics of claim 1.
This arrangement of the switching elements permits the positive detection of a driver""s intention so that for example a deactivation of the brake power assistance during the transition from an emergency braking to a directed braking. xe2x80x9cEmergency brakingxe2x80x9d means a braking operation with the shortest stopping distance, whereas xe2x80x9cdirected brakingxe2x80x9d refers to a braking operation before reaching a certain obstacle.
Further properties and advantages of the invention will be explained in the following description of embodiments with reference to the accompanying drawings in which: